1. Field of the Invention
The present invention relates to an image recording apparatus, more particularly to an apparatus wherein one-component, conductive and magnetic developer (hereinafter simply called a "toner") is imagewisely deposited on a recording material directly in response to electric image signals.
2. Description of the Prior Art
An image recording apparatus of this type is known, as disclosed in U.S. Pat. No. 3,816,840, which will be briefly described with FIG. 1. The apparatus comprises a toner container 2 and a stationary toner carrying member 1 which is dipped in the powder of conductive and magnetic toner T. The toner carrying member is in the form of a cylinder of non-magnetic material. In carrying member 1, there is a magnet 3, as magnetic field generating means, which is rotatable in the direction of arrow A and which has magnetic poles of opposite polarities equidistantly spaced around the circumference thereof. A recording electrode assembly 4 is provided, including an array of electrode elements which are electrically isolated from each other and extended on the surface of the toner carrying member along the axis thereof. The electrode elements are made of a conductive and magnetic material, such as permalloy, nickel and iron. Opposed to the recording electrode 4, a recording material 5 is moved in the direction of arrow B. The recording material is shown as consisting of a conductive base plate 5a and a dielectric layer 5b thereon, but not limited to this type. Commercially available electrostatic recording paper is usable.
Across the recording material 5 from the recording electrode 4, there is provided a backing roller electrode 6 which is in contact with the conductive base plate 5a of the recording material 5. The apparatus further comprises a doctor blade 7 and an image signal source 9. The reference numeral 8 designates a recording station where the recording is effected.
In operation, the magnet 3 is rotated in the direction of the arrow A, while the recording material 5 is moved in the direction of the arrow B, by unshown conventional driving mechanisms. The rotation of the magnet 3 moves the toner on the carrying member 1 by the function of the magnetic field thereof in the direction shown by arrow A'. The toner T, while being moved thereon, is subjected to a regulating function of the doctor blade 7 secured to the container 2 at its outlet so that the toner is formed into a thin layer of uniform thickness. Thereafter, the toner T is conveyed to the recordihg station 8, whereat the tips of the recording electrodes are opposed to the backing electrode 6, and they are erected in the form of chains on the tips of the recording electrode so as to contact the surface of the recording material 5. In this state, upon a signal voltage applied between the electordes 4 and 6 from the signal source, the electric charge injected into the toner particle, which is on the surface of the recording material 5, through the chain of the toner particle, is electrostatically attracted by the electric charge injected to the neighborhood of the back of the dielectric layer 5b, so that the toner is held on the surface of the dielectric layer 5b of the recording material 5. This forms an image in accordance with the image signal. The resultant image is heat-fixed or pressure-fixed on the recording material 5 by an unshown fixing device.
Referring now to FIG. 2, another conventional image recording apparatus is shown, such as those known by U.S. application Ser. No. 22859. Since this is similar to the system described with FIG. 1, except for the portions which will be described, the detailed description of the similar parts is omitted for the sake of simplicity by assigning the same reference numerals are assigned to the elements having the corresponding functions.
A recording material 5 is a cylinder having a conductive base plate 5a and a dielectric layer 5b thereon. It is rotatable in the direction of arrow Z. In a toner container 12, there is powder of toner T into which a stationary toner applying roller of a non-magnetic material is dipped. In the toner applying roller, there is a rotatable magnet 11 which is driven by an unshown driving mechanism. A recording electrode assembly 4 includes a number of electrode elements opposed to the recording material 5. The electrode elements are made of a conductive and magnetic material. The electrode 4 is sandwiched by magnets 15 having opposing N poles and outside S poles, for example.
When the magnet 11 rotates in the direction of arrow C, the conductive magnetic toner T moves from the container 12 on the applying roller 10 in the direction of arrow D and is subjected to a regulating function of a doctor blade 7 to become a thin layer, which is conveyed toward the recording material 3. Between the recording material 5 and the toner applying roller 10, a voltage is applied by the power source 13, so that the toner T is attached to the recording material surface by electrostatic force to form a thin layer thereon. The thin coated toner layer is conveyed, by the rotation of the recording material 5, to the recording station 8, at which the toner particles are formed into chains extending to reach to the tips of the recording electrode 4. The contact of the toner to the electrode 4 discharge the charge having been injected by the applying roller 10 through the chains of the toner particles and the recording electrode 4, so that there is now no attracting force between the recording material 5 and the toner T. At this instance, if an imagewise signal voltage is applied between the recording material 5 and the recording electrode 4 from the signal source 9, an electric charge appears in the surface toner through the chains of the toner particles, as explained with respect to FIG. 1. The electric charge cooperates with the charge at the back of the dielectric layer 5b to hold the toner T on the recording material 5. Then, the unattached toner T is removed, without disturbing the imagewisely attached toner T, by a toner remover 14, such as those using a magnetic attraction or air flow to leave the attached toner T. By doing so, a visualized image appears.
However, it has been found by the inventors that those conventional systems involve a problem from the standpoint of high resolution image. The problem is that, if the spacing between the adjacent electrode elements is reduced in order to enhance the resolution, the distance between the recording electrode 4 and the recording material must also be reduced, correspondingly. This makes it difficult to embody the system.